If 3) holds, then \(\pi n l/\gamma \)  denotes a rational number of degrees, and, according to [1]}, the inclusion
\(\tan \frac{\pi n l}{\gamma } \in (\mathbb {R} \setminus \mathbb {Q}) \cup \lbrace  0\rbrace  \cup \lbrace  \pm 1 \rbrace \) 
